Biometric authentication systems are used for authenticating users of devices incorporating the authentication systems. Among other things, biometric sensing technology can provide a reliable, non-intrusive way to verify individual identity for authentication purposes.
Fingerprints, like various other biometric characteristics, are based on unalterable personal characteristics and thus are a reliable mechanism to identify individuals. There are many potential applications for utilization of biometric and fingerprints sensors. For example, electronic fingerprint sensors may be used to provide access control in stationary applications, such as security checkpoints. Electronic fingerprint sensors may also be used to provide access control in portable applications, such as portable computers, personal data assistants (PDAs), cell phones, gaming devices, navigation devices, information appliances, data storage devices, and the like. Accordingly, some applications, particularly portable applications, may require electronic fingerprint sensing systems that are compact, highly reliable, and inexpensive.
Constantly scanning a fingerprint sensor array to capture an image may unnecessarily consume power when there is no corresponding fingerprint to be imaged. To minimize power consumption, a fingerprint presence detection system is sometimes used to detect the presence of a finger before entering a higher power fingerprint imaging mode. One way to do this is to use additional dedicated presence detection sensing elements alongside the sensor array. However, these dedicated elements can be inaccurate and take up valuable device real estate.
In view of the above, there is a need for a finger presence detection system of a fingerprint sensor that provides an accurate indication of finger presence over a sensor, while allowing for the sensor to be smaller or the sensing area to be increased. These and other advantages of the disclosure, as well as additional inventive features, will be apparent from the description of the disclosure provided herein.